Multiwire Branch Circuits

摘要

Are multiwire branch circuits becoming antiquated for most new installations, or are they still being used in most circuit applications? Changes have been made in the last few National Electrical Code (NEC) editions to ensure circuits supplying critical loads-such as those provided for operating room and critical-care equipment in hospitals, exhaust fans for uninterruptible power supply system battery rooms, and emergency and other life safety equipment-will have individual nonmultiwire branch circuits. Disconnecting the power at one circuit breaker supplying a bank of lights at a patient bed location should not interrupt power to lights for other patient bed locations. Critical equipment and lighting cannot be indiscriminately disconnected from power if that shut down will affect other similar circuits.